The field of this invention lies in techniques for reducing magnetic hysteresis losses in thin magnetic tapes.
It is known that amorphous metal alloys can be produced from a melt of corresponding composition by cooling the melt so rapidly that it solidifies without crystallization. By such a quenching procedure such alloys can be directly formed in the shape of a thin tape or ribbon, whose thickness, for example, can range up to several hundredths of a millimeter and whose width, for example, can range up several millimeters (compare, for example German Offenlegungschrift No. 25 00 846 and German Offenlegungsschrift No. 26 06 581).
Amorphous alloys can be distinguished from crystal alloys be means of X-ray diffraction measurements. Thus, in contrast to crystalline materials, which exhibit characteristic sharp (intense) diffraction bands, the intensity of X-ray diffraction bands exhibited by amorphous metal alloys is found to alter with the diffraction angle, only slowly as is comparable to the characteristic X-ray diffraction patterns observed in liquids or common glass. Depending upon the production (conditions), an amorphous metal alloy can be totally amorphous, or it can be comprised of a two-phase mixture of the amorphous and the crystalline states. Thus, the term "amorphous metal alloys", or equivalent as used herein, generally has reference to an alloy which is at least 50%, and preferably at least 80%, amorphous on a 100 total weight percent alloy basis.
Each amorphous metal alloy has a characteristic temperature, the so-called "crystallization temperature", such that, if the amorphous alloy is heated to, or above, this temperature, said alloy passes into its crystalline state. However, the amorphous condition is retained during thermal treatments below such crystallization temperature.
The soft-magnetic amorphous metal alloys known up to the present time are characterized by having the general composition EQU M.sub.y X.sub.1-y,
where M represents at least one of the metals iron, cobalt and nickel, and X represents at least one of the so-called glass-forming elements boron, carbon, silicon and/or phorphorus, and y is a numerical value which lies between 0.60 and 0.95. In addition to the metals M, such amorphous alloys can also contain additional metals, particularly, titanium, zirconium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, manganese, palladium, platinum, copper, silver and/or gold. In addition to the glass-forming elements X, or, optionally, even in place of such elements, such an amorphous alloy can contain the elements aluminum, gallium, indium, germanium, tin, arsenic, antimony, bismuth and/or beryllium (compare German Offenlegungsschrift No. 25 46 676, German Offenlegungsschrift No. 25 53 003, German Offenlegungsschrift No. 26 05 615 and German Offenlegungsschrift No. 26 28 362).
Soft-magnetic amorphous alloys with their respective associated magnetic properties are of great interest for technical utilization since they, as previously mentioned, can be directly produced in the shape of thin tapes. In contrast thereto, in the case of the crystalline soft-magnetic metal alloys now common in the art, a plurality of milling steps with numerous intermediate annealings are required in order to produce correspondingly thin tapes. By the term "soft magnetic" as used herein reference is had to such an alloy which is relatively easily magnetized or demagnetized.
It is known that the magnetic properties of a soft-magnetic amorphous metal alloy can be altered by means of a heat treatment at a temperature below its crystallization temperature. Thus, in the case of the members of a series of cobalt-containing soft-magnetic amorphous metal alloys, a corresponding heat treatment in conjunction with helium in a magnetic field running parallel to the longitudinal direction of the treated tape, a so-called longitudinal field, which is sufficient in order to saturate the alloy technically, leads to an increased remanence and to a decreased coercive force. A corresponding heat treatment of the members of such series of alloys in a magnetic field running vertically (or perpendicularly) to the longitudinal direction of the treated tape, and parallel to the plane of the tape, a so-called transverse field, leads to a treated tape whose magnetization varies in an approximately linear fashion with respect to the field intensity for field intensity values of nearly zero (German Offenlegungsschrift No. 25 46 676).
It was ascertained with more intensive examinations of tapes, and cylindrical cores formed thereof, the tapes consisting of the soft-magnetic amorphous alloy Fe.sub.0.40 Ni.sub.0.40 P.sub.0.14 B.sub.0.06, that an annealing treatment at a temperature between the Curie temperature and the crystallization temperature for such alloy leads to a mechanical relaxation of the alloy, and that the magnetic properties of the correspondingly treated alloy depend considerably upon the conditions under which that alloy is cooled to a temperature below its Curie temperature subsequent to its annealing treatment. The annealing treatments in these known experiments were carried out in conjunction with nitrogen and in a vacuum. By annealing followed by a subsequent controlled cooling in a magnetic longitudinal field, the remanence and the remanence ratio, as is common is crystalline soft-magnetic materials, was increased in relation to non-annealed cores. In contrast thereto, but as is also common in crystalline soft-magnetic cores, the remanence and the remanence ratio in relation to non-annealed cores was decreased by means of annealing and subsequent cooling in a transverse magnetic field, so that the corresponding inductance-field intensity curves have a flatter (smoother) gradient than those of the unannealed cores, and exhibit a so-called F-characteristic due to their flat (shallow gradient) course. In an annealing treatment in conjunction with nitrogen, moreover, the coercive force and the magnetic hysteresis losses were considerably decreased in relation to the unannealed cores, whereas the corresponding effects were somewhat less salient (pronounced) in the case of the annealing in a vacuum (compare IEEE Transactions on Magnetics, Vol. Mag-11, No. 6, 1975, pages 1644 through 1649 and conference on Rapidly Quenched Metals, Vol. 1, Boston, 1975, pages 467 ff.).
By annealing in nitrogen, with one exception, the magnetic hysteresis losses in these known experiments, however, could only be decreased to values which are approximately double the magnetic hysteresis losses in tapes consisting of comparable soft magnetic alloys. Thus, for example, in an alternating magnetic field at a maximum induction of 0.1 T, and at a frequency of 10 kHz, in the most favorable instance, loss values of 18 mW/cm.sup.3 equal to 2.4 W/kg were obtained, whereas the corresponding losses in tapes consisting of low-loss conventional crystalline soft-magnetic alloys only amount to approximately 1 W/kg. Only in the one case mentioned was a loss value of approximately 1.33 W/kg obtained in alternating cited magnetic field. However, the core involved has been cooled with a high cooling speed which is virtually no longer capable of being technically controlled, and, moreover, it exhibited a remanence ratio of 0.2 which no longer results in a flat (shallow) F-loop. However, for a number of technical uses, which up to now were reserved for crystalline soft-magnetic alloys, precisely a hysteresis curve in the form of an F-loop is desirable in simultaneous conjunction with magnetic hysteresis losses which are as low as possible.